Low-pressure arc discharge lamps have been used for optical display of information, including alphanumerics, graphics and moving or still pictures, on a large screen. Such a display consists of a matrix of picture elements, or pixels. Each picture element includes a monochrome light source in the case of a monochrome display. In the case of a color information display, each picture element includes three lamps of the primary colors: red, green and blue. Each lamp is selectively energized on a scale ranging from off to full brightness to produce one of the primary colors or a mixture of primary colors for that picture element.
A large screen display of the above-described type is disclosed in U.S. Pat. No. 4,559,480, issued Dec. 17, 1985 to Nobs. The disclosed display utilizes picture elements each consisting of three discharge tubes coated with different phosphors to produce the primary colors. The disclosed display has sufficient brightness for use in outdoor sports stadiums and the like during the daytime. Such displays have typically utilized compact, generally U-shaped fluorescent lamps that are primarily used for general illumination. The envelope includes at least two longitudinally extending tubes joined together by a transversely extending envelope portion. Examples of such lamps which are commercially available are the "twin tube" and "double twin tube" fluorescent lamps manufactured by GTE Sylvania, Danvers, Mass. Other examples of such lamps are disclosed in U.S. Pat. No. 4,426,602, issued Jan. 17, 1984 to Mollet et al and U.S. Pat. No. 4,481,442, issued Nov. 6, 1984 to Albrecht et al. In these lamps, the surface brightness along the envelope is substantially constant, and much of the radiation is emitted in a direction that cannot be utilized in the picture display. Low-pressure arc discharge lamps wherein a large portion of the light emitted from the lamp is directed through end faces of parallel tubes are disclosed in pending application Ser. Nos. 064,978, and 064,731, both filed June 22, 1987, and in U.S. Pat. No. 4,786,841, all and assigned to the assignee of the present application. The disclosed lamps can include different color phosphors.
A large screen picture display of the type used in a sports stadium consists of several thousand picture elements, each including three discharge lamps. In the past, the discharge lamps have been individually soldered to circuit boards located at the rear of the display. When one or more of the lamps in the display failed, it was necessary to remove an entire circuit board from the display, to unsolder and remove the defective bulb and then to solder a new lamp in its place. Finally, the circuit board was replaced in the display. Such a procedure was found to be inconvenient in the environment of a sports stadium. The use of connectors for single U-shaped fluorescent lamps is disclosed in the aforementioned Pat. Nos. 4,426,602 and 4,481,442. Such single connectors are not satisfactory for use in picture displays due to the spacing between lamps necessitated by the dimensions of the plug-in base. In order to form a picture element having a satisfactory appearance, it is necessary for the red, green and blue lamps to be closely spaced or in contact with each other. Any spacing between the lamps of a pixel degrades the apparent uniformity of the picture display. Furthermore, single lamp connectors are inconvenient in the case of a large screen display due to the large number of single lamps and the possibility of replacing a lamp with the wrong color.
A further difficulty with prior art picture displays has been the necessity for baffling between picture elements. Light was emitted through the sides of the lamps in each picture element, causing undesired illumination of adjacent picture elements.
In prior art picture displays of the above-described type, it has been difficult to obtain good quality color at an acceptable cost. Due to the large number of elements in a picture display, it is necessary that the lamps of each picture element be relatively low in cost. When phosphors in an acceptable price range are utilized, the green lamp often appears bluish and the red lamp may be pink. It is desirable in such picture displays to provide high quality color at an acceptable cost.
A further challenge in large screen picture displays is to provide a picture that has a high quality appearance to viewers close to the display and to viewers that are located far away from the display. It will be understood that in a sports stadium, some of the viewers are likely to be located relatively close to the display screen. Any defects are more apparent to a viewer that is close to the screen.
Depending on the size of the display screen, each picture element may have viewing surface dimensions in the range from less than one inch to about three inches. For viewers that are located a considerable distance from the display, the light from the three lamps of a picture element is combined by the eye and the brain to produce the illusion of a single color. However, for viewers that are relatively close to the display screen, picture elements appear as a collection of spots of different colors. Furthermore, when a straight line or a geometric figure having changes in color along its length is displayed, the offset in the positions of the lamps within each picture element produces a line that is offset at the point where the color changes.
It is a general object of the present invention to provide picture element lamp assemblies for use in large screen information display systems.
It is another object of the present invention to provide a plug in picture element lamp assembly containing red, green and blue discharge lamps.
It is a further object of the present invention to provide a picture element lamp assembly for an information display system that has high color quality.
It is a further object of the present invention to provide a picture element lamp assembly that is easily replaceable.
It is yet another object of the present invention to provide a picture element lamp assembly having a filter for correcting the colors emitted by low-pressure arc discharge lamps.
It is still another object of the invention to provide a picture element lamp assembly having a combination of the above features.